Shoji Takigami

Hydration characteristics of the gum exudate from Acacia senegal

Abstract Using Differential Scanning Calorimetry the interaction of water with the gum exudate from Acacia senegal can be investigated. The first water molecules bind strongly to the hydrophilic groups of the core carbohydrate structure and are non-freezing. As the water content is increased several metastable freezing-bound states can be identified. One transition at ~255 K does not change with increasing water content. This metastable freezing-bound water state is closely associated with the polysaccharide structure. The transition of the main freezing-bound state, however, moves towards that of free water with increasing water content. This broad transition embraces at least two other metastable states, which can be recognised by variations in thermal history. There is one freezing-bound state at ~268 K and an accompanying metastable state which readily converts to free water on heating at 323 K, but when left to stand at room temperature this metastable state re-forms. Overall, A. Senegal can be seen to have a structure which effectively binds water. The freezing-bound states do not overlap with free water until ~20% solution has formed. From the Δ H value of the transitions it is evident that the binding of water is a necessary driving force not only in the conventional confectionary applications, but also in emulsification when the protein core performs the contrasting hydrophobic directive force.

Hydration characteristics of the cross-linked hyaluronan derivative hylan

Abstract The ability of hylan, the formaldehyde cross-linked derivative of hyaluronan, to interact with water has been studied using differential scanning calorimetry (DSC). Three types of water can be distinguished: non-freezing, freezing-bound and free . When the water content of the system is increased, even by up to 10%, almost all the water remains in the freezing-bound state, with a ΔH value less than free water. Several metastable states of water can be detected within the structured hylan-water matrix, indicative of defects in the frozen-bound ice structure. The maximum amount of non-freezing water, intimately associated with the hydrophilic groups of hylan, corresponds to 13 mol water per disaccharide unit of the hyaluronan chain. The large capacity shown by hyaluronan entangled networks to build water into their structure could also be responsible for their unusually high viscosity and elasticity after the onset of entanglement. Such viscoelastic properties are the basis for their use in viscosupplementation of arthritic diseased joints.

Effect of preparation method on the hydration characteristics of hylan and comparison with another highly cross-linked polysaccharide, gum arabic

Abstract The water binding characteristics of hylan are compared with another cross-linked polysaccharide Acacia Senegal gum exudate ( A. Senegal ) using differential scanning calorimetry. Both polysaccharide systems bind water effectively, and the transitions characteristic of two types of freezing-bound water can be distinguished from the melting or freezing of free water. There is evidence for the existance of metastable states of freezing-bound water within the two systems. Gum arabic binds considerably less freezing-bound water than hylan systems. A. Senegal does not have the same ability as hyaluronic acid to form structured entangled networks which can incorporate water within the matrix. The hylan samples are of two types: hylan fluid where the hyaluronan chains are crosslinked with formaldehyde, and hylan gel where the cross-linking agent is vinyl sulphone. The hylan gel retains the freezing-bound state of water as a stable thermodynamic state ca 20–50% more effectively than hylan prepared from the freeze-dried solid prepared from either concentrated or dilute hylan fluid. The traps formed from freeze-dried hylan gel are also more stable. Hylan gel prepared by precipitation with isopropanol and freeze-dried is the most effective hylan sample for stabilising the freezing bound state. For this material even in ~6% solution the vast majority of the water is retained in the freezing-bound form.

Selective permeability of grafted nylon-6 membranes: 1. Permeability of urea and potassium chloride in acrylamide and acrylic acid grafted membranes

Abstract The permeability of urea and potassium chloride through γ-irradiated nylon-6 membranes grafted with acrylamide (AM) and acrylic acid (AA) was investigated. The permeability of urea and potassium chloride through both AM and AA grafted membranes increased with increases in the levels of grafting. The diffusion of urea and potassium chloride through AA and AM grafted membranes (with more than 100% grafting) can be explained by the free volume concept. However, this explanation does not apply to potassium chloride permeating through AA-grafted membranes. The diffusion of potassium chloride through highly swollen AA-grafted membrane obeys the free volume concept outwardly, however the diffusion is modified by the concentration dependence of the permeant.

Konjac glucomannan-based hydrogel with hyaluronic acid as a candidate for a novel scaffold for chondrocyte culture

Chondrocytes were cultured using konjac glucomannan (KGM) and hyaluronic acid (HA) as a scaffold for cartilage regeneration. They were subsequently compared with scaffolds produced using agarose hydrogels. Chondrocytes derived from Japanese white rabbits were cultured: 2.0 × 105 cells were seeded on KGM containing hyaluronic acid (KGM/HA) and agarose and cultured for 5 days. Their viability was assayed using WST‐8 procedures; the ultimate stress and modulus of elasticity of each construct was calculated. After 3 days of cultivation, mRNA in chondrocytes, such as collagen types I and II and aggrecan, were measured using RT‐PCR. Both chondrocyte‐seeded constructs were stained with safranin O/fast green and were evaluated histologically. Chondrocyte viability decreased concomitantly with increasing KGM/HA or agarose concentration and with culture time. Cell viability in 2% agarose was significantly lower than that in 2% KGM/HA on the third and fifth days (p < 0.05). The primary elastic modulus increased concomitantly with increasing polysaccharide concentration. Elastic moduli of 2% KGM/HA with chondrocytes (0.389 ± 0.119 N/mm2) showed little difference from those without chondrocytes (0.283 ± 0.243 N/mm2), although those of 2% agarose with chondrocytes (0.403 ± 0.094 N/mm2) were significantly lower than those without chondrocytes (0.736 ± 0.227 N/mm2; p < 0.05). Collagen type II mRNA expression was higher in KGM/HA and agarose than in monolayer cultures, although KGM/HA had lower aggrecan mRNA expression levels than did agarose. Histological tests of KGM/HA–chondrocyte constructs revealed chondrocyte aggregation and proteoglycan production in the pericellular region. The results show that KGM/HA might be useful for chondrocyte culture. Copyright

The state of water in nylon-6 membranes grafted with hydrophilic monomers: 2. Water in acrylic acid, acrylamide and p-styrenesulphonic acid grafted nylon-6 membranes

Abstract The state of sorbed water in nylon-6 membranes grafted with acrylic acid (AA), acrylamide (AM) and p -styrenesulphonic acid (SS) was investigated by differential scanning calorimetry. There are three kinds of water in AA- and AM-grafted nylon-6 membranes: non-freezing water, intermediate water and free water. The SS-grafted nylon-6 membrane retains both non-freezing water and freezing water. In the latter, the intermediate water and the free water cannot be distinguished. Each kind of grafted membrane with high extent of grafting can retain a good deal of the non-freezing water and the intermediate water. This is due to an increase in the content of hydrophilic repeat units as graft copolymerization progresses. The SS repeat unit can retain a larger amount of water than can AA or AM. It was also found that the amount of non-freezing water per repeat unit increased in the order of AA-, AM- and SS-grafted nylon-6 membranes. The order reflects the nature of the homopolymers.

Microscopical studies of the tissue structure of konjac tubers

Abstract The tissue structures of 2-year-old konjac tubers were investigated using a variable pressure scanning electron microscope equipped with an energy-dispersive X-ray spectrometer and an optical microscope. Konjac mannan (KM) cells are distributed all over the tuber and the spaces between the KM cells are filled with parenchyma. The KM cells are covered with scale-like cell walls and the size of the cells varies from 160 to 650 μ m. Other kinds of particles with different sizes are observed in the honeycombed cells around the KM cells. The small grains relate to protein granules and the spherical particles (~12 μ m in diameter), which are composed of small granules (1–3 μ m in diameter), are starch. The tuber also contains potassium and calcium in the parenchyma. Most calcium is found in the needle-like crystals in the form of calcium oxalate. Such crystals are also found in 1 year and seed tubers.

E.s.r. study of the conformational transition of spin-labelled xanthan gum in aqueous solution

The order to disorder transition of xanthan molecules in aqueous solutions has been studied using e.s.r. spectroscopy. Nitroxide spin-label was covalently attached to carboxyl groups on the xanthan side chains. The e.s.r. spectra obtained for aqueous spin-labelled xanthan solutions at varying ionic strengths contained both isotropic and anisotropic components at room temperature. The anisotropic component was attributed to the association of the side chains with the xanthan cellulosic backbone and was found to be present in greater proportions at increasing ionic strength. The spectra gradually changed with rising temperature and the proportion of anisotropic component decreased. This spectral change reflected the disruption of the side chain association with the backbone during the conformational change. Hysteresis effects were observed following sequential heating and cooling cycles suggesting that chain aggregation occurred.

Selective permeability of grafted nylon-6 membranes: 2. Potassium chloride permeation in acrylic acid grafted membranes

Abstract The permeation of potassium chloride through γ-irradicated nylon-6 membranes grafted with acrylic acid (AA) was investigated. The permeability of potassium chloride increases with increasing levels grafting in the membrane. It was found that the theory of permeation of electrolyte through ionic membranes (derived from the phenomenological equation) was applicable to the permeation of potassium chloride through AA-grafted membrane with high levels of grafting. The effective concentration of fixed charge determined by the Donnan membrane equilibrium exhibited almost the same value in the grafted membrane regardless of the levels of grafting. It was found that a tortuosity factor was dominant through affecting the permeation of KCI through the membrane. This may be considered as an interference factor in a homogeneous membrane.

Enthalpies of water in freezing and thawing of wool-water mixtures

Enthalpies of freezing and thawing of water in wool-water mixtures are evaluated by DSC. The two different samples are clean wool extracted with acetone and delipided wool prepared by extraction with a mixed solvent composed of chloroform, ethanol, and water in volume ratios of 19:8:1. On cooling curves at 5 K/min for both samples, there are three main peaks for crystallization at about 228, 240, and 255K. The enthalpy of water corresponding to each peak is determined from the slope of the linear relationship between heat and water content. The enthalpies estimated from the three exotherms are 17, 181, and 287 J/g of water, respectively, for the acetone extracted wool, and the values for the delipided wool are 17, 85, and 281 J/g. On the heating curves, there are two peaks—a broad endotherm beginning at a temperature of T d, which varies with the water content, and a sharp peak due to melting of ice for bulk water at 273K. The respective enthalpies are 222 and 330 J/g for the acetone-extracted wool and 110 and 326 J/g for the delipided wool. A possible explanation is proposed for the marked difference in enthalpy between the samples upon freezing and thawing. Removing the unbound internal lipids increases diffusion resistance to water transport within the fibers. The relationship of Td to water content is also discussed.